Exemplary embodiments of the present invention relate to a valve train for an internal combustion engine with a cam unit arranged on a camshaft in a rotation-resistant and axially displaceable manner.
The function of a camshaft is to control the gas exchange valves of an internal combustion engine. In order to be able to carry this out as efficiently as possible and depending on operating parameters of the internal combustion engine, today's camshafts have in part axially displaceable cam units with several different cam (stroke) profiles. The different cam (stroke) profiles of the cam units, which act on the respective gas exchange valve, are thereby characterized in a different manner or embodied with a different stroke (course) and in extreme cases have no marked stroke curve (zero stroke), but merely a basic circle radius, which renders possible a selective cylinder switch off.
EP 0 798 451 B1 discloses a valve train having a camshaft with cams for actuating gas exchange valves, wherein at least one cam is provided with several cam paths arranged axially one behind the other and arranged in a rotation-resistant but axially displaceable manner on the camshaft. The cam has a so-called stroke profile, which interacts with an actuating element for displacing the cam, wherein the stroke profile is embodied on the cam and the actuating element has an actuating pin, which is to be brought into engagement with the stroke profile in a displaceable manner radially to the camshaft. In the illustrated exemplary embodiment the cam has a total of three cam paths arranged next to one another, wherein the cam, starting from a central operating position in which the central cam path is active, is displaceable by one step to the left or by one step to the right. For this purpose, the cam has respectively one stroke curve on its two outer cylindrical ends. By engagement of a first actuating pin assigned to its stroke curve on the front side, the cam can thereby be displaced in a first axial displacement direction, and can be displaced back against this working direction again via a second actuating pin, which interacts on the opposite end of the cam with another stroke curve.
DE 42 30 877 A1 discloses a cam block arranged on a camshaft in a rotation-resistant and axially displaceable manner with two cam paths arranged axially next to one another, wherein, for the purpose of the axial displacement of the cam block, this cam block interacts with its contoured front face with the contoured front face of an adjacent pressure ring, as soon as the pressure ring is blocked via a catch hook engaging radially in the pressure ring.
DE 10 2004 011 586 A1 discloses another embodiment of an axially displaceable cam unit having several cam paths arranged next to one another.
Exemplary embodiments of the present invention provide a valve train for an internal combustion engine, which valve train guarantees a very specific control of the internal combustion engine depending on different operating parameters and is thereby structurally embodied such that the necessary installation space inside the internal combustion engine is reduced compared to embodiments hitherto known or can be sized as small as possible. Furthermore, exemplary embodiments of the present invention provide cam units with more than two axially adjacent different cam path profiles in a space-saving manner.
A valve train according to the invention comprises a camshaft with a cam unit supported in a rotation-resistant and axially displaceable manner for actuating a gas exchange valve, wherein the cam unit has at least two cam paths arranged axially one behind the other (one next to the other). In one aspect of the present invention the cam unit has a plurality n of cam paths where n≧3. Furthermore, the cam unit according to the invention has an actuating profile, which interacts with an actuating element that is displaceable between a home position and an actuating position radially to the axis of the camshaft (and arranged in a stationary manner in a housing part of the internal combustion engine) for the purpose of the (stepwise) axial displacement of the cam unit on the camshaft. According to the invention, the actuating profile of the cam unit is formed by the lateral front face thereof. According to the invention, the actuating element of the cam unit is embodied as with an (in particular as with a plurality (n−1) of) actuating pin(s) displaceable in the radial direction between the home position and the actuating position, wherein the at least one actuating pin interacts with the lateral front face of the cam unit such that an axial lateral displacement of the cam unit on the camshaft takes place. In each position of the cam unit a different cam path is thereby activated for actuating the gas exchange valve (or in each step a different cam path to actuate the gas exchange valve interacts with the cam follower for actuating the gas exchange valve).
In different, further aspects of the present invention the actuating element can have either a plurality of separate actuating pins (individually displaceable in a radial manner) arranged axially (directly) next to one another or a plurality of actuating pins (individually displaceable in a radial manner) arranged coaxially to one another. It is essential to the invention thereby that the (effective) actuating area provided by the actuating element (or by the individual actuating pins thereof), arranged on one side of the cam unit and interacting with the lateral front face of the cam unit through the switching of the at least one actuating pin, is shifted or moves once—or preferably multiple times in the same displacement direction.
The cam unit can have a corresponding actuating profile on both lateral front faces, so that a separate actuating element, in particular switchable in a multiple-step manner, is respectively assigned to both lateral front faces of the cam unit. This ensures forced guidance or forced displacement in both displacement directions. Alternatively, the cam unit can have an actuating profile interacting with the actuating element on only one front face, and on its other front face can be embodied in an essentially planar manner and can be acted on with a spring force via a spring element (return spring) against the displacement direction. The invention is explained in more detail below based on an exemplary embodiment shown in a drawing FIGURE.